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Guide to Using the Australian Archean Mafic-Ultramafic Magmatic Events Map

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Guide to Using the Australian Archean Mafic-Ultramafic Magmatic Events Map GEOSCIENCE AUSTRALIA Guide to Using the Australian Archean Mafic-Ultramafic Magmatic Events Map Record Dean M. Hoatson, Subhash Jaireth, Alan J. Whitaker, David C. Champion, and Jonathan C. Claoué-Long 2009/41 APPLYING GEOSCIENCE TO AUSTRALIA’S MOST IMPORTANT CHALLENGES Guide to Using the Australian Archean Mafic-Ultramafic Magmatic Events Map GEOSCIENCE AUSTRALIA RECORD 2009/41 by 1 1 1 1 1 Dean M. Hoatson , Subhash Jaireth , Alan J. Whitaker , David C. Champion , and Jonathan C. Claoué-Long 1. Onshore Energy and Minerals Division, Geoscience Australia, GPO Box 378, Canberra, ACT 2601 i Department of Resources, Energy and Tourism Minister for Resources and Energy: The Hon. Martin Ferguson, AM MP Secretary: Mr John Pierce Geoscience Australia A/g Chief Executive Officer: Dr Chris Pigram © Commonwealth of Australia, 2009 This work is copyright. Apart from any fair dealings for the purpose of study, research, criticism, or review, as permitted under the Copyright Act 1968, no part may be reproduced by any process without written permission. Copyright is the responsibility of the Chief Executive Officer, Geoscience Australia. Requests and enquiries should be directed to the Chief Executive Officer, Geoscience Australia, GPO Box 378 Canberra ACT 2601. Geoscience Australia has tried to make the information in this product as accurate as possible. However, it does not guarantee that the information is totally accurate or complete. Therefore, you should not solely rely on this information when making a commercial decision. ISSN 1448-2177 ISBN 978 1 921672 49 1 (hardcopy) ISBN 978 1 921672 50 7 (CD-ROM) ISBN 978 1 921672 51 4 (webcopy) GeoCat # 69935 Bibliographic reference: Hoatson, D.M., Jaireth, S., Whitaker, A.J., Champion, D.C. and Claoué-Long, J.C., 2009. Guide to using the Australian Archean mafic-ultramafic magmatic events map. Geoscience Australia Record 2009/41, 135 pp. Cover Illustration: Part of the ‘Australian Archean Mafic-Ultramafic Magmatic Events: Yilgarn Craton, Western Australia (Sheet 2 of 2)’ map. This map, which is based on the interpretation of aeromagnetic data, depicts outcropping mafic-ultramafic igneous rocks, layered mafic-ultramafic intrusions, and interpreted subsurface extensions of equivalent rocks under cover in the northeastern corner of the Yilgarn Craton. The Archean greenstone sequences are depicted by a green screen for outcrop and stipple for undercover. The interpreted margin of the Yilgarn Craton is indicated by a dashed pink line. The inset photographs are bladed (top) and comb (bottom) spinifex textures that are distinctive features of Archean komatiitic rocks that are important hosts of nickel sulphides. Contents Executive Summary .......................................................................................................... 1 Aims and Scope of Study ................................................................................................. 3 Distribution of Archean Mafic-Ultramafic Igneous Rocks in Australia ............................ 4 Archean Large Igneous Provinces...................................................................................11 Methods .......................................................................................................................... 13 Sources of Geochronological Data and Digital Datasets ....................................................................13 Characterisation of Mafic-Ultramafic Rock Units..............................................................................13 Characterisation of Mineral Deposit Types ........................................................................................14 Definition of Magmatic Events...........................................................................................................14 Spatial Representation of Magmatic Events .......................................................................................15 GIS Techniques...................................................................................................................................16 Maps and Reports........................................................................................................... 17 Components of the Map.................................................................................................. 21 Australian Archean Mafic-Ultramafic Magmatic Events Map: Sheet 1 .............................................21 Australian Archean Mafic-Ultramafic Magmatic Events Map: Sheet 2 .............................................23 Conclusions.................................................................................................................... 26 Acknowledgements................................................................................................................................29 References ..............................................................................................................................................30 Appendices: Appendix 1. Digital Geological and Geophysical Datasets Used in this Study ......................................38 Appendix 2. Attributes, Definitions, and Values Used for Characterising Archean Mafic-Ultramafic Units in Appendix 11 (Spreadsheets: Age and Setting)......................................................................40 Appendix 3. Revised Classification of Deposit Types Associated with Mafic-Ultramafic Rocks..........45 Appendix 4. Type Examples of Archean Mafic-Ultramafic Magmatic Events...................Facing page 46 Appendix 5. Time–Space–Event Chart ...............................................................................Facing page 46 Appendix 6. Additional Ages and Other Geological Data on Sheet 1 ....................................................47 Appendix 7. Compositional Data of Komatiitic Rocks from the Yilgarn Craton ...................................50 Appendix 8. Important Publications Containing Geochronological Data ...............................................52 iii Appendix 9. References used for the Australian Archean Mafic-Ultramafic Magmatic Events Study.. 57 Appendix 10. Time-Slice Maps of Archean Mafic-Ultramafic Magmatic Events ................................. 70 Appendix 11. Geological and Geochronological Data of Archean Mafic-Ultramafic Rock Units in Australia (Excel spreadsheets—a CD is provided for hardcopies in pocket attached to Record) Figures: Figure 1. Generalised geology of Australia .............................................................................................. 6 Figure 2. Major geological and tectonic subdivisions............................................................................... 7 Figure 3. Distribution of type examples of Archean Magmatic Events with time.................................. 18 Figure 4. Distribution of type examples of Proterozoic Magmatic Events with time............................. 19 iviv Executive Summary This Record provides information to assist in the use of two web-based map sheets (Hoatson et al. 2009a,b) that show the continental extent and age relationships of Archean mafic and ultramafic rocks and associated mineral deposits throughout Australia. The Archean Eon, as recently ratified by the International Commission on Stratigraphy (www.stratigraphy.org), extends from ~4000 million years to 2500 million years (or Ma) (Gradstein et al., 2004; Ogg et al., 2008). Archean mafic and ultramafic igneous rocks with reliable ages in Australia are largely confined to the older crustal components in Western Australia and South Australia. In this study, twenty-six Archean Magmatic Events (AME) ranging in age from the Eoarchean ~3730 Ma (AME 1) to the late Neoarchean ~2520 Ma (AME 26) have been identified in the Yilgarn and Pilbara cratons, Sylvania Inlier, and Hamersley Basin of Western Australia, and the Gawler Craton of South Australia. The Archean time period in Australia is noteworthy for some of the largest layered mafic-ultramafic intrusions (e.g., Windimurra, Munni Munni, Gidley Granophyre), extensive continental flood basalts (various mafic volcanic formations in the Fortescue Group) and coeval mafic dyke swarms (Black Range Dolerite), differentiated mafic sills (Golden Mile Dolerite), and the widespread occurrence of primitive olivine- bearing ultramafic rocks called komatiites (Kambalda Komatiite) which contain world-class deposits of nickel sulphides (Kambalda, Mount Keith, Perseverance). The Archean mafic-ultramafic magmatic record for Australia commences with the ~3730 Ma Manfred Event in the Narryer Terrane of the Yilgarn Craton. Gabbroic rocks in the Manfred Complex are the oldest known rocks in Australia that have been dated. The Narryer Terrane appears to be anomalous (exotic accreted origin?) in its age context relative to the other terranes of the Yilgarn Craton. Mafic- ultramafic magmatic events in the Pilbara Craton spanning the interval ~3500 million years to ~2925 million years have a relatively wide frequency, occurring every ~20 to ~200 million years. In contrast, the Neoarchean period from ~2820 million years to ~2665 million years represents an extremely busy evolutionary phase with multiple overlapping coeval events recorded for the Pilbara and Yilgarn cratons, Hamersley Basin, and Sylvania Inlier. During this ~160 million year period, fifteen mafic and ultramafic magmatic events occur every ~10 to ~15 million years in the magmatic event record. This dynamic period appears to represent a continuum of magmatic events which may not be accurately resolved
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